STUDIES IN PLANT RESPIEATION AND PHOTOSYNTHESIS. 7 



reverse occurs. In this connection it is interesting to note that 

 according to the experiments of Deleano^ it is claimed that when 

 leaves {Vitis vinifera at 18° to 20°) are kept in the dark, these util- 

 ize only carbohydrates during the first hundred hours; thereafter 

 drastic disturbances in the proteinaceous components of the leaf 

 occur. The carbohydrates thus act in the nature of protein-sparers. 

 Now, Meyer points out that when leaves are kept in the dark for a 

 long time, the chloroplast apparatus becomes so greatly impaired 

 through loss of protein that, on subsequently placing the leaves in 

 the Hght, photosynthesis is no longer sufficiently active to produce 

 enough material to cover the nocturnal loss through respiration. 

 Meyer's observation of decreasing protein-content with advancing 

 age of the leaves is especially interesting when compared with the 

 studies of Nicolas,^ who found that on the basis of respiration coeffi- 

 cients the energy release in young leaves is considerably higher than 

 in old ones. 



According to Emmerhng, there is with advancing age only a 

 reduction of amino nitrogen and total nitrogen but not of protein 

 nitrogen. This latter observation is in even closer accord with the 

 hypotheses of a causal connection between amino-acid content and 

 respiration. Also, the carbohydrate-content shows a general increase 

 as the leaves grow older.^ These facts indicate that carbohydrate- 

 content alone can not be taken as an index of the rate of respiration ; 

 nor, obviously, can the carbohydrate-content serve as a measure of 

 the photosynthetic activity. 



The following analyses taken from Czapek {Biochemie der PHanzen, 

 1st ed., Vol. II, p. 202) indicate the amounts of protein which have 

 been found in leaves. These values have, however, only a limited 

 significance, because in the analysis neither the age of the leaves, 

 their history, nor the environic conditions were taken into consider- 

 ation. 



Table 1. 



1 Deleano, N. Jahrh. f. wiss. Bot., 51, 541-592 (1912). 

 » Nicolas, G. Reo. Gen. Bot., 30, 210-225 (1918). 

 MiCHEi/-DuKAND, E. lUd., 30,337-345, 377-382 (1918); 



251-268, 287-317 (1919). 

 » Emmerung, E. Landw. Verauch. Stat., 34, 113 (1880). 



31, 10-27, 53-60, 143-156, 196-204, 



